1. Field of the Invention
The present invention relates generally to a printing apparatus and, more particularly, to a printing apparatus using an order-separation type optical modulator, which allows a plurality of diffracted beams, which are formed to have a plurality of diffraction orders and are derived from a single beam by reflection and diffraction, to scan divided scanning areas according to diffraction order, thus improving resolution.
2. Description of the Related Art
Printer technology is being developed towards high speed, compactness, high quality and low price. A general printer employs a laser-scanning scheme that performs scanning using a Laser Diode (LD) and an f-θ lens.
To implement a high-speed printer, an image head scheme that uses a multi-beam type beam-forming device is employed. In such a scheme, high speed and high quality can be achieved, but a problem occurs in that cost is high because a plurality of light sources must be used.
FIG. 1 illustrates an example of a conventional laser-scanning scheme that uses a single light source and an f-θ lens. With reference to FIG. 1, the operation of the conventional laser-scanning scheme is described below.
A light beam is generated by an LD 10 in response to a video signal, passed through a collimator lens 12 and then converted into parallel light. Thereafter, the converted parallel light is converted into linear light, which is parallel to a scanning direction, by a cylinder lens 13 and is then incident on a polygon mirror 14.
As described above, in the case in which the linear light, which is parallel to a scanning direction, enters through the cylinder lens 13, the polygon mirror 14 rotated by a motor scans the entering linear light in a direction towards the f-θ lens 15.
Thereafter, the linear light scanned at a uniform angular velocity by the polygon mirror 14 is deflected in a scanning direction, experiences aberration correction and, therefore, is scanned on a scanning area at uniform velocity.
It is difficult for the above-described scanning scheme to achieve high-speed printing due to a slow switching speed and the scanning speed of the polygon mirror 14.
That is, in order to increase the scanning speed of the light beam, the polygon mirror 14 must be rotated using a high-speed motor. However, in this case, there are problems in that the high-speed motor is high in price, and operational reliability is lowered because the motor, which rotates at high speed, causes heat, vibration and noise, so that an improvement of scanning speed cannot be expected.
For another method of improving the speed of an optical scanning device, there is an image head printing scheme using a multi-beam type beam-forming device.
That is, as shown in FIG. 2, a multi-beam is formed by constructing a Light Emitting Diode (LED) array 21 on an image head 17 such that a printing paper may be fully covered by LEDs 22, so that printing can be performed one line at a time without the use of the polygon mirror and the f-θ lens, unlike the laser scanning scheme and, therefore, printing speed can be remarkably improved.
However, in the case in which a plurality of LEDs is used to form the LED array 21, there are problems in that cost increases, and uniform images cannot be acquired because optical uniformity among the LEDs of the array is degraded.